A hydrolaccolith - also called pingo - is "a perennial
frost mound consisting of a core of massive ice, produced primarily by injection
of water, and covered with soil and vegetation" (Everdingen 2002). These
pingos occur in continuous and discontinuous permafrost zones. The term is used
to describe relatively large features with heights of 10 m or more and horizontal
dimensions of more than 100 m. Most pingos are conical, somewhat asymmetric,
and have a circular or oval base and a fissured top that may be cratered. The
fissures and craters are the result of rupturing of the soil and vegetation
cover during doming due to progressive development of the ice core (Everdingen
2002). In Russia they are formed on the bottom of dried or drying lake depressions
and can reach 40 to 70 metres in height. In the presence of ground water the
pingo appears with an ice core inside (Kotlyakov & Khromova 2002).
In the past Russian scientists made a drilling investigation. After that the active unfrozen layer has a thickness of 5 metres and consists primarily of clay and sand sediments and contains continental molluscs (Bukharov; personal comment). Because of the height over ground the laccolith was estimated to have a vertical extension of 50 to 100 metres, assuming the pingo has a water content of 30 percent and has no ice core. This estimation was derived from the expansion of ice at the prevailing gradient of temperature between water and ice. If the pingo consisted of ice, the vertical extension would be lower.
Everdingen, Robert van (ed) (2002) Multi-language glossary of permafrost and related ground-ice terms. Boulder, CO: National Snow and Ice Data Center/World Data Center for Glaciology. Side 56.
© B. Merkel <firstname.lastname@example.org>, 29.11.2004, http://www.geo.tu-freiberg.de/studenten/Baikal_2004/baikalexcursion/hydrogeology/overview/hydrolaccolith.HTM